This is only going to be useful to a smaller number of people, but I’ve been singing in a choral society for my entire adult life. My favorite thing is singing in harmony with other singers. One of the things I do to practice to make sure I really know my part, is to go to one of many online sites which upload all the different voice parts for various choral pieces.
If we’re working on Mozart’s Requiem for instance, I’ll play the alto part and then sing my part (soprano 2). You can’t do it well unless you know your part, because you can’t hear anyone else singing your part.
The thing is, this is really fun. It’s like singing a duet with someone. I love doing it and I do it just for the fun of it, even if I don’t need to practice.
Choir is over for now, because of COVID-19, and I really miss that community, and the exquisite feeling of harmony. For me it’s one of the best feelings in the world. So when I feel sad or isolated I go to places like the Chord Perfect channel on YouTube: https://bit.ly/3eLDUNw
And I’ll pick one of my favorite pieces and sing along.